I can sympathise. I have been here, a few times! I can often take a while to reach orgasm. I'd say average is 20-30 minutes, sometimes as quick as 2 mins and sometimes hours..(Not kidding.) For the first year of my relationship living with my current partner, I could not orgasm with him at all and even doing it alone became hard work. I discovered I lost my orgasm due to medication I was taking and then because I lost it for so long, I ended up constantly thinking about it during sex and mentally blocked myself from getting there.
One piece of advice I really want to push on you is that you have to try your best not to think about this too much and worry about it because the mind is POWERFUL and it can make it become a worse problem. On the other hand, the power of the mind can help you resolve it quicker.
First thing I want to say regarding what is happening for you, is that you are totally 100% normal. Woman on average take much longer than men to reach orgasm. You don't have a problem and you need to look at it this way:
He was a very lucky man to be with a woman in the past who could orgasm quickly or at the drop of a hat!
Because I can tell you straight up, many women are simply not that responsive. I am one of them. I have also had my confidence shattered by men telling me their tongue hurts, or making comments to suggest I "take too long" What is "too long" anyway? If we sit down to enjoy a 3 course meal at a restaurant, do we rush through the starter and main course, wolf down the pudding and raise out hands at the speed in which we just did it? Nope! We relish it, we soak in the atmosphere, we indulge in all the tastes and sounds and smells and we do not force it down and rush to the end.
That also begs the question: What is the end? The issue with viewing orgasm as the end goal, the thing to be achieved, is that when it doesnt happen, everyone feels like a failure. We then rule out the fact that we just enjoyed some amazing pleasure, our skin tingling, sharing intimacy and sensations all because we did not achieve something. Orgasm is the cherry on top, but the experience, the foreplay is all part of the delicious cake. The word foreplay insinuates that everything before penetration and orgasm is just a warm up to the main event. Not true though.
As a woman, who has been where you are and experienced extremely similar things, I can tell you that orgasm will be harder to achieve, if not almost impossible, when you are worrying about him being in pain, worrying he is bored, worrying your taking too long, worrying you won't cum, worrying he will be disappointed...etc etc. So my advice would be to explain to him that orgasm does not equal good sex and it is the experience that feels amazing. Both of you need to remove focus on your lack of orgasm, back up a little and enjoy the whole experience of intimacy. In fact, if you both try having sessions where orgasm is BANNED...and the focus is to give each other as much pleasure as possible, you might find it helps remove pressure.
Also you must understand that all women are different in what they need to cum. It takes me about 20 to 30 minutes to orgasm and that used to be much longer. My partner complained he was in pain after one session, Now we can have much longer oral sessions, which he enjoys, because he changed his technique. My guy used to stick his tongue out as far as possible and wiggle it fast. No one can keep that up for ages. In the end I asked him to slow right down and to get his face all up in my business. When he wasn't over reaching with his tongue, he stopped experiencing that pain.
Unfortunately there is no guarantee or a foolproof way to ensure you reach orgasm. My main tips are for you to stop worrying about it because you are completely normal and pressuring yourself WILL make it harder. To speak with your guy and have him understand it isnt all about the O, but the whole experience and lack of orgasm does not mean lack of enjoyment and pleasure. Also I recommend guiding him and asking him to slow down and be kind to his tongue, but if this makes oral too slow and gentle for you, then I recommend getting really close first, or just not using oral as your go-to method for orgasm. There is nothing wrong with needing more. Some women can only reach orgasm from strong vibes ONLY! There is NOTHING wrong with that. Next I recommend removing the pressure to orgasm by both having sessions where orgasms are banned and the idea is just to tease each other. I also recommend that you (and him) understand that just because one woman could orgasm from his oral, doesnt mean they all will. We are all different.
The fact you can orgasm alone, but not with a partner, sounds very similar to what I went through and again I just want to push the fact that the mind is an extremely powerful thing. People will say to you "relax" "Dont think about things" "Stop worrying" but that is so much harder to do than to say. It will take time and I got there through talking with my partner, honestly. I told him how I felt, my worries, we experimented, it failed - often, we talked more, sometimes the talking made it worse! but over time I had to learn and train myself to relax and let go. It isn't easy and it won't happen overnight. Try to see every step in the right direction as a huge positive and any step in the wrong direction (eg: You orgasm once then not again for a few months) as something minor. If you can push all the worry and thoughts from your mind, it really helps.
Keep talking to him, tell him all this, take it slow, remove the pressure and keep enjoying the sessions you have now. try not to feel bitter or angry at yourself if you fail to orgasm. Treat orgasm as the cherry on top of the cake and not the be all and end all. If it never happens for you, please be aware you are not alone. So so many women are in the same position and you are not a failure. If you simply need more stimulation, have you tried a vibrator during your sessions with him? If you can start enjoying orgasms, through methods that you know are almost guaranteed, like using a vibe, or doing it yourself, then do that...with him. Use the vibe during, play with yourself during. Some women just need very specific things done to them and find it really difficult or impossible to orgasm from someone elses touch. That's okay too.
Anyway, rambled on a bit...oops. Hope this helps xx