Why do guys struggle with emotions for girls?

He ONLY teases me & people comment that he's always around me. He has no problem going to lunch w other female coworkers but for me, he gets nervous & anxious makes sure people are with us. Alone, he's very sweet. One coworker recently asked if something was between us becuz we flirt. Ij convo w others about what we did on the weekend or what not, we will only tell people "my friend and I did this..." or "my friend lent me their shirt to wear." Versus saying eachothers names. It's secretive but nothing has happened & we haven't been phsycial.
Lately, we have been starting to argue more, lots of misunderstandings, walking around eggshells. I've been down lately & had wanted to see him for my birthday. He went over the top for me last year. This year he did nothing & it hurt. He even told our close friend he f ed up for not making an effort. He never told me this & instead he blamed me talking about how hurt he was because I spent a few days distant, not wanting to talk about it or anything. He was super upset when he called me & when I said I felt like he didn't want me around or that he didn't really care, he got angry and upset & kept saying how hurt and insulted he was and hung up on me. Finally, yesterday he decides he wants to talk. This wasn't the person I know though. He was rigid. Like all the emotions of anger and hurt from last week disappeared. Suddenly he declared we are just work friends. That he only treats me like everyone else. That I'm strange and to stop being weird. He kept repeating ( an excessive 20+ times) that we just work together and to stop being weird. That is wasn't like we were dating or something and had to discuss any personal issues. He was just in total denial mode. i did tell him that i was sorry he was so hurt the week before that he means so much to me & care for him. He was silent, rigid. Every time things get too emotional he backs away, denies everything & I am left feeling rejected & wounded.

Updates
9 mo
Every time, after we go through this, he almost immediately tries harder. He comes back full force flirting, teasing, calling, texting, facetime. I notice him watching me more, ill look up & he's staring, others notice, our close mutual friend notices that if i walk by and theyre talking, he will lose all train of thought as he just watches me walk away or watch what im doing. Ill find him even MORE trying to always be around me. I've even hid & he will ask people where I am or seek me out
Updates
9 mo
I'm not sure how to navigate as we have had several conversations these last few years. Anything from you mean everything to me and no one else to I don't know what you're talking about, I just work with you. This time around I did say this is so hard (w no context) and maybe I should just quit and not work here. That REALLY upset him.
Why do guys struggle with emotions for girls?
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