I am sorry to hear about your problem - I have the same problem as you too and like you I suffered alone and in silence for a long time.
I would urge you 100% to tell your new boyfriend about this problem. I told mine in 'installments' - at first I told him I get panic attacks and when I do they give me an upset tummy, but I feel embarrassed to have an upset tummy in public. Then I kind of gave him more and more detail over the months that followed in little snippets, until now, finally he knows the whole actual truth. For me that truth is that I DO get anxious sometimes and it upsets my stomach, but I also get anxious whenever I feel like I need to poop away from home. It doesn't matter if my stomach is playing up or not - I can't go (unless I can find a super private toilet. I cannot go at his four bedroomed detached house which makes spending time together very stressful and hard for me!). This is because I worry that it takes me a long time to go when my stomach is playing up and also because I get a lot of noisy gas. So basically I worry that he will hear me break wind!
The thing is, he has been really sweet about me telling him and at each new 'stage' of the truth has been very kind and loving. He has said that it does not matter and that if he heard me breaking wind in the bathroom or he knew I had an upset tummy, it would not bother him at all and he would still love me.
I have cried a lot while telling him about it and I still do cry when I feel I need to go at his house. I have only actually managed to go once on a VERY relaxed and laid back day and when I was having normal bowel movements. BUT even though it hasn't made a practical difference to me yet, I feel much better for having told him about it and now he understands the problem. Although I still worry about it a lot with him, I feel like maybe if on a given day I was feeling quite close to him I would now be able to tell him that I needed the toilet and ask him to sit in the lounge with the television on top volume. I haven't done it yet and I know I will cry a lot if and when I do, but now he has seen how vulnerable this makes me and how much it worries me, he has said he will give me lots of hugs and kisses after if I ever do go to the toilet at his house.
I also try to 'practise' being in the bathroom where I tell him I am going for bathroom practise and just go and sit in there for 10 mins. I'm not very good at that because I feel like I need to be really quiet and sometimes that in itself makes me anxious, but at least maybe one day I might be able to say I'm practising and go and do the real thing?!
I wish I could bring myself to break wind in front of him once or twice and laugh about it, but I don't feel I can. I would cry so so much if I ever broke wind in front of him and would be so embarrassed and ashamed.
But really, I would encourage you 100% to tell your boyfriend. I feel much better since telling mine and doing that has even given me the confidence to tell another close friend. And you know what? Neither of them laughed. And both of them told me that it doesn't matter and shared a story of when they pooped their pants.
I think maybe telling your boyfriend might at least make that one area of your life a little bit easier, even if it doesn't solve it right away. I am still trying to overcome my problem, but I would love to have just one person who I could totally relax with and that can only come when I learn to poop in the same house as them!
Good luck xxx