What type of therapy should I look for?

This is harrassment.

You might think this is the OP being infatuated………………can you imagine how the female co-worker feels?

HSE Guidelines on Sexual Harrassment in the workplace.

https://www2.hse.ie/mental-health/life-situations-events/bullying-harassment/sexual-harassment-work

I am surprised at how lenient, helpful and understanding everyone here has tried to be so far with this poster. He is clearly a stalker, he is sexually harrassing a colleague. This is serious. The fact that he can start off by saying he is not going to take anything a counsellor says on board, he has tried it, its not working is a flag. This is not someone open to help. This is someone who is able to argue back every single point and still insist he is in love and can prove it to this woman!

This level of being able to turn an argument around makes me think of coercion, of manipulation of assertion and it is wrong.

Even the amount of time the OP has spent here yesterday arguing his point shows a level of obsession. This is a grown adult with a child yet he is obsessing over a female work colleague who has said NO on numerous occasions and he is still trying to PROVE his love. This is extremely unhealthy and quite frankly dangerous to the woman involved. NO means NO!