I Need To Confess

I know its anonymous but I need to confess about cheating. I've been with my gf since we were 15 but when I was 18 and my gf E was 19 we had a bug fight and she walked out and stayed with a friend for the night even though her mum was coming round for dinner . When E's mum turned up I was in pieces so she cooked us food and talked to me about it and agreed the E was in the wrong. Her mum was only 35 and is a milf she looked more like an older sister. She started to hug my head to her chest and because of how big her breasts are and the cut to her top my face was in-between them. When she let me up she noticed I was erect and said it's fine, she takes it as a compliment but would happily take it any way. At 1stvi thought she was playing or maybe it was too much wine with dinner. She smiled and excused herself to the toilet and when she came back she was naked, in a panic I just said wow E definitely gets her body from you and before I could stop her she'd gone to her knees and put me in her mouth running her tongue around the head and then deep throat ing it which E said couldn't be done because it was to long. I stopped thinking of reasons to stop and went with it. We ended up having sex in every room just because we could and I came in her, then we had sex again as soon as I could get it back up thus time finishing on her face and tits something else E wouldn't let me do. Afterwards I said she could sleep in the bed but I'd take the sofa incase E came home which she agreed was a good idea but during the night as I passed the open door I saw her naked with no covers and her ass looked so good I woke her up licking her tiny little asshole before fucking her pussy then when I was about to cum I pulled out and managed to get the head in her ass before I emptied my balls again which she seemed to love. I let her go back to sleep after and when I woke up in the morning E was home and they'd talked and she apologised to me which led to amazing make up sex after. Her mum occasionally still mentions what we did but aside from the odd touch or squeeze here and there we haven't done it again and E doesn't know anything about it.
We're getting married this year before our first child is born and I just needed to share.