Xander was not an incel. From Urban Dictionary: incel means "a person (usually male) who has a horrible personality and treats women like sexual objects and thinks his lack of a sex life comes from being "ugly" when its really just his blatant sexism and terrible attitude. incels have little to no self awareness; even when they see other "ugly" men with girlfriends, they consider these men to be tricksters who have somehow beat the system and can get women despite being cursed with unattractiveness (in other words, they're respectful to women and women are attracted to their personalities, but incels cant comprehend such a phenomenon). they believe that women owe them sex, and many of the more extreme incels like to spend time in incel communities on the internet coming up with ways to make women have sex with them (often involving genocide of people of color, genocide of "Chads" (men who have sex), taking rights away from women, raping them, having sex with women's dead bodies, and other horrid, disgusting things. they cant understand that that is PRECISELY why women want nothing to do with them)."In the early seasons he acts like Buffy 'owes' him something more than friendship and generally behaves like an entitled incel.
Xander is attracted to Buffy, but he never acts like she owes him sex. People keep throwing these new fancy terms at Xander when most of them don't really apply. In the good old days, it used to be "Nice Guy", but when you look at the show closely, you'll see that Xander never stated that he deserves Buffy. He wishes that Buffy would notice him, but he never told her or told anyone that Buffy should be with him because he’s a good guy.
Xander never expects any rewards from Buffy. He saved her life more than I could count and never asked for a thank you much less used those times to get into her pants.
Xander can be an immature jerk and he does treat Buffy in regards to Angel horribly. He admits that he did in Amends, and from that episode, he stops doing it. He also reacted badly to Buffy sleeping with Spike, and he does admit that to Buffy in Seeing Red, and in S7 after living with Spike, Xander becomes objective about Spike. He doesn't join Anya and Dawn into hating Spike and he clears Spike's name.
Xander was actually interested in Willow. The almost kiss in When She Was Bad proves that, his jealousy over Willow dating Oz, and his "I love you" in Becoming Part 2. He probably tries to ignore his attraction to Willow because he's scared he'll lose her if they break up.I also find it horrible how he messes with Willow's feelings: all these years he must have known or at least suspected she was in love with him, and he was never interested. Then all of a sudden, when she's not available anymore, he has to have her. Cheating on Cordelia in the process, of course.
I do agree with you that Xander did treat Buffy and Willow horribly on occasions, but IMO the good outweigh the bad. Xander was the one who did not give up on Buffy in Prophecy Girl even though she had rejected him ( how incel of him, right? ) and saved Buffy's life. Xander was the one who offered himself to Ampata as sacrifice to save Willow's life in Inca Mummy Girl. Putting your life in danger to save the people you love is a huge thing, and not that many people are capable of that, but it never stopped Xander when it came to Buffy and Willow.
I agree with @WillowFromBuffy . I thought Xander was a lovely boyfriend, but not a perfect one, who is anyway? Anya wasn't a perfect girlfriend either. How many times does Xander have to tell her to keep their sex life private? She never respected his wishes and blurted about them anyway. How many times does she keep insulting his friends?And don't even get me started on what he does to Anya. Throughout their relationship, he spends so much time putting her down, making her feel like she's not behaving in the 'right' way, acting like he's always just a little bit ashamed of her.
Yes, Anya would not survive in the human world if it weren't for Xander guiding her through it. Once she aggravated Giles so much, he considered firing her if it weren't for Xander stepping in.