Catching partner telling me little “white” lies

Hi all, since the beginning of my (23F) relationship with my partner (34M) I’ve caught him multiple times on telling me little lies that honestly make no sense. We’ve been together for 3 years, engaged for almost a year by now. Overall we’re a really happy couple, but I think just like everyone we both come with our own baggage. I’ve gone to therapy and managed to work through majority of my issues and have been encouraging him to do the same as he’s had a hard life (parents emigrated with him as a child to flee war, his mum sadly passed away from cancer when he was 16, he’s an older a sibling out of 3 so he became the second parent once his mum was no longer there). I think I’m a very understanding person but I’ve had some resentment building up in me over the past year and a bit, here’s some examples why (although there’s been countless times where I’ve caught him just making things up or leaving important detail which once revealed changes the story drastically)

- I’m bi and we’ve had a threesome with a girl (which was totally my idea), yet whenever I see him looking at other girls he always denies doing so.

- In the beginning of us talking with each other (before going official obviously) he lied to me about living with his ex at the time.

- most recent one: I’m currently traveling for work and in a different city, he said he was going to get a steak for dinner last night by himself. He then proceeded to send me a photo where I could see someones plate directly opposite to his - I asked confused who it was as 20 min ago on the phone he said he’s going by himself. He told me he’s sitting across some random lol which obviously I didn’t believe cause in the photo I could see at least 10 empty seats around them. Turns out he was with a friend (male, whom I know).

I just don’t understand why he does that? It makes me so angry because 1. I don’t get the reasoning behind his actions, 2. He’s promised me countless times he’ll go to therapy to fix his issues but never does, 3. I feel stupid and like I’m overreacting since majority of the time it’s not a big deal but it genuinely bothers me, especially the excuses he comes up with once called out.

I love him but I’m honestly really hurt, and sometimes I get paranoid that he’s maybe lying to me about something big too but I just haven’t caught on.