Search Results: hard to notice flirting

Something I've noticed about myself is that I have a hard time settling down. I tend to fixate on one person, start a relationship with them, and get bored with it a few months later. It's during this period of boredom that I usually find myself interested in flirting with other people, while I still have extreme affection for the person I'm dating.
My last relationship had a few periods like this, and though I still felt completely in love with my boyfriend, I always wanted more. I hate this about myself, and I certainly can't stand being single, but sometimes relationships can be a bit slow and it drives me crazy.
I won't deny I enjoy attention, and as someone with a lot of anxiety concerning myself and how others see me, I will constantly search for attention and approval when I feel like it's lacking from my current relationship. So I guess my biggest question is, if I have no intentions of leaving the person I am with currently, is it still bad to engage in harmless flirting during relationship "lulls"?

I have known this guy for 11 years and have always had a crush on him. But not sure how he feels. Things I've noticed:

He would always ask to meet up with me for coffee last year and would want to know what was happening in my life. He would send me selfies and pictures of what he does in his day. He would also share a lot with me in terms of what he does in his day. We would be there for each other even if we didn't get to see each other much. When he's busy with work, he said "you know you can annoy me, I won't mind. Just like how I'll unhesitatingly annoy you, and you won't mind!"or "you are one of the few people I would go out of my way for"

However, one time when I talked to him about having an older brother, he jokingly said "That's just like me, right?" I told him that I never thought of him as my older brother. And he said " okay, you're like a younger sis" (this was only once) and then recently he called me bro.

BUT THEN weeks ago when I wanted to meet up, he would say he was busy because he was resigning from his job and his company was moving offices. I backed off. Then one day on his Instagram I saw that this girl (who already has a bf) had tagged him in two photos-one was on a coffee meet up they had had and the other was a cake they had made for their work party. And she was flirting with him hard on Instagram which made me upset. As a result, I got jealous and confronted him about it and asked if they were going out. He said no. But then when I asked if he was going to ask her out, he said "Oh. um, maybe?"

Then last week it seemed like he hated me & he began acting as a prick. He started to ask questions about whether my ex boyfriend and I were still together. I told him it was over & had no idea where this change in attitude came from or why he asked. I got upset & asked him why he was acting like a prick. He apologised and said "I didn't mean to come off as an arrogant jerk you should know me better than that I would go out of my way to hurt you."