I(21F) feel like I am cheating on my partner(21M) because of a past situation

So before my current boyfriend and I were official, at this point we were not seeing other people but we weren’t official yet. I had no intensions of dating or seeing anyone else because I really liked him and knew that if he wanted to be with me I was in for it too.
However one night, many of my friends and I were at my home and as the night passed mostly everyone left, except one guy friend of mine. It’s important to state that this guy and I had a small history with having feelings and kissing. I wanted him to leave but he kept walking around my house asking if he should stay longer. I just told him its up to him, if he’s feeling sick he can stay in the bed and I’ll go outside and wait and then he can leave. I wasn’t sure if he was drunk or something so I didn’t want to push it. I just stayed away. I really didn’t want anything to happen and I just wanted to deescalate the situation and get the night over with.

Eventually, I was sitting on my bed and he suddenly came and layed on my lap for a few seconds. It felt really wrong and I felt very uncomfortable but I didn’t yell. After a few seconds of processing I asked him to get up.

Then before leaving he told me he still had feelings and I told him that its best if he leaves now and closed the door. At that time, my current partner wasn’t that close to me and I thought he would misunderstand and hence I didn’t tell him all the details, just overall that this guy wasn’t leaving and expressed his feelings.

Anyways he didn’t react much that time. And recently it came up and I told him that there was such an incident and he totally freaked out. I felt awful. I felt like I should have told him this had happened when it did. And since then I just feel super guilty.

I didn’t mean for it to happen, I didn’t want that guy to be in my space but I was scared of how he would react and did what I thought was best to not cause any conflict and made him leave.
Since then I’ve been very careful about him, I don’t try to associate or be around him. I don’t want that type of feeling.

After my boyfriend’s reaction, I feel torn. I wanted to protect myself in that situation cus I was alone and now I feel like the worst person in the world. We have been officially together for 7 months now and I want nothing more than to be married to this man.

How do I forgive myself and be a better partner?