Somewhat quick question

What are the ethics of suddenly making out with Person X, when you were invited a few hours before to Person Y’s house, who may or may not have wanted to have sex with you, and who you like, and who may or may not like you back, and who you are trying to enter a relationship, and when Person X is also trying to enter a relationship, and is the best friend of your ex, who is probably over you but might not be? I know it’s very long-winded, but it’s been plaguing me for the last 24 hours.