I do think there are parallels, for a couple different reasons, some already mentioned.
1. I do think the fellas themselves, once completely "humanized", did feel threatened by Buffy being stronger/more capable than them. It's in a male's genetic code to "protect the female", so it was probably difficult for them to over come that, especially when they had both been supercharged for so long. This issue showed more with Riley of course, but I do believe both wouldn't have felt as needed by Buffy in any aspect - she is a pretty closed off person emotionally and doesn't readily ask for help with anything in life, so where would that leave her boyfriend if they can't fight along with her?
2. As far as Buffy, she has carried the burden of being the Slayer for years. She is always in danger, fighting, killing, getting beaten on - a pretty high-stress gig. Add to that a boyfriend that can't handle himself in combat situations adds one more thing for her to worry about. Riley seemed more capable of fighting, but she had to be more aware of both he and Angel's weakness in those situations, thus giving her more weight to carry. That had to be on her mind somewhere along the road. She already had to watch over her friends that were out helping her, as well.
I do think it would be possible for a relationship between Buffy and a regular Joe could work, but it would be difficult. He would need to know why she was always working nights and coming home beat up. He would have to learn to keep his nose out of it so she wouldn't have to be worrying about his safety. (Also, I do think Buffy having a significant other/kids lends the bad guys opportunities to get at her more easily. Kidnapping, hurting, killing her family.) The issue with both Riley and Angel is that they were accustomed to be in the fight, with and without Buffy, so it was hard for them to just walk away from what they had been doing their whole lives.