Threesomes and open relationships

Hey all! Been a while.

So some background. I came out properly about 2 years ago (I'm 22) and 6 months ago got into my first proper relationship after sleeping around a bit.

I am very much in love with him. He's smart, extremely attractive and runs the student LGBT society at my university (where I am affectionately referred to as first lady). He's also one of the kindest and most understanding people I've ever met. He is a few years younger than me (20 at the moment) but a lot more experienced with relationships and sex than me. He has been patient enough to let me grow and we now have what I think is a healthy relationship and sex life. We've already been on holiday together and met each others' families.

My question however is on the subject of monogamy. When we first met I was relatively open to the idea of an open relationship. Before I met him I considered myself essentially aromantic so it was a simple thought to consider but he said he wasn't interested in the idea - possibly, he says, because he'd recently come out of a long term (year and a half) relationship where he was cheated on.

However, more recently he's been open to the idea but the more I've fallen for him, the more I consider it with discomfort. I used to be so relaxed but now even when I notice him looking at another guy it makes me anxious. I know this is completely unreasonable and unfair on him as I often do exactly the same. We both often point out hot guys to each other.

I hate that my brain reads a huge amount into tiny things that he's said too. For example I interpret him saying something like "I feel hot" as "I am hotter than you and will leave you when I find somebody hotter." I have a pretty significant inferiority complex and see myself as unattractive compared to him (he probably is slightly more attractive but not enough to reasonably cause insecurity.) I will interpret "that guy is checking me out" as "I am going to leave you for that guy." This is despite the fact he CONSTANTLY tells me he loves me and, although he is now a bit more open minded about the idea of an open relationship, he would never cheat on me.

I think a lot of this has originated from us becoming semi-long distance in recent months. I am spending a year in a different university which is about and hour and a half drive away. He socialises often with other LGBT people (including his ex who cheated on him) because of his position in the university and I do at the society in my current university too but I get very anxious when we are apart and he is out partying without me.

Part of me thinks the obvious, practical and most sane solution to my insecurity would be an open relationship. We've already agreed that making out with someone in a club doesn't constitute cheating (as long as we tell each other afterwards). I'm mostly okay with this but visualising it does make me quite anxious too. I wonder whether a threesome might relax me a bit too?

Will these thought processes just improve with time? It's frustrating that my brain can't see the situation logically and sanely. This post comes across as a rambling rant because it's not really clear in my head and I just wondered if anyone else has similar experiences? It's so odd that I've fallen so hard for somebody when I never had crushes before! I really love him and don't want to lose him because I come across as overbearing!