I was with my ex boyfriend for 6 years (from 17 to 23) and we broke up May 2020 as I found out he was on Tinder talking to another woman. I felt sure that I wouldn't get back with him as it was the 3rd or 4th time that I'd found out that he was talking to other women in the space of 9 months. The first time was August 2019, he had made a move on another woman who he worked with and was messaging her on social media the morning after working a shift with her all night. He denied it until he couldn't deny it any longer as the evidence was there. I broke up with him for a week and gave him another chance as it was the first time. Although, I saw that he has added another woman from a volunteer group he was a part of. I didn't see their messages as it was blank, but her name on social media was very fruity.
We broke up again for 3 months - Nov 2019 until Feb 2020 as he kept on lying to me and putting his friends before me. I found out that he had made a move on another woman less than 2 weeks after we broke up when he went to a guys weekend away with his friends. We were back together from Feb 2020 until May 2020 until I found out in May 2020 that he was on Tinder messaging another woman again. I ended things and didn't speak to him for 3 months until he showed up at my house begging for me to take him back after begging me through email from the day we'd broken up.
It's been 8 months since we broke up now and I still love him and he loves me. I've had time to get over him speaking to other women. I understand that he is young (24 almost 25) and made mistakes and I put a lot of pressure on him, I've recently been diagnosed with BPD so I understand why I put so much pressure on him now (not that it's an excuse). I wouldn't mind getting back with him. However, I feel extremely guilty as I slept with another guy 2 months after we broke up for the final time as I believed I was completely done with him. The guy I slept with used me as he became distant after we had sex and it took me months to get over it as he was only the second guy I had ever had sex with. I ended up blocking the guy after 2 weeks of him being distant (not answering my calls) and only messaging me here and there. I had to go to counselling to get over being led on and used.
I feel guilty as, before, my ex was the only guy I had ever had sex with and now I feel disgusting. I can never tell my ex, but I feel guilty. My mother advised that I don't tell him. My friend said I should tell him because he was the only person I had slept with before (but she doesn't give the best advice and actually made me feel more guilty and anxious).
How can I stop this extreme guilt without confessing to my ex, if we do get back together?
Please help.