What then do you do- judgement is fine!!?

Have you guys ever been through this, I'm really annoyed- I am not a home wrecker and I would not ever cheat on my partner- there has been this guy who contacted me for a business propaganda and ever since we spoke two weeks ago- It's really weird cause as I said I would not cheat or do anything as I have a partner and he has a girlfriend! I am in a tumultuous relationship of five years I have been trying to fix the last 2 years- where my partner admittedly sais he is not picking up his half to do anything to fix it though is "trying" to not be so selfish- this guy who contacted me through a work propaganda has already told me about his open relationship with his partner- they have s and quite an open relationship- though I told him I was not interested in any kind of ual relationship- He said not a problem- though is just sooo easy to talk to!! He does not judge me actually listens to what I say and rang me to give advice one day when he sais he could hear in my voice I was upset (over my partner) and genuinely chatted to me not getting ual but actually just related to me on my level- From the way he speaks to me he sais- 'It so weird cause I never been able to talk to anybody as openly as we have' I totally agree cause we are just very straight up people and it's o.k- and even though sais I'm 'Great value, and really cool chick to talk to' I get that these are warning signs and red flags, though this person and I get along so well it's fricken annoying- What should I do- I want to get him out of my head though I can't, and I know me well enough to not ever cheat with him even though he has an open relationship- It's a moral thing I would not ever do this to my partner- You can not fall for someone after 2 weeks- I refuse to believe it though unfortunately in such a short time- because we totally understand and get along with each other, there's just been an instant bond-What is your opinion?