I fully that most people posting here make use of irony. But I find it damning that behind all of those post there is likely to be a kernel of truth.
I really hope your guy are just posting random anime girls and not actual "love" you once had. That would be as young humans says, cringe.
"young humans"
I think you're just as out of touch as unironic waifuists (which I don't think anyone here is)
Firstly, it's not the pixels, it's the idea behind them.
Secondly, an unironic waifuist actually puts their waifu in the same mental 'place' as a real significant other.
The semi-ironic waifuism on the Internet today is more a statement of what imagined character is the most appealing to you, where they are put in a 'place' not replacing any real relationships (potential or otherwise) but are put in a place distinctly designated as the position of "waifu"
This place implies either that they are who you would be with if they were real, or they are the partner of an imaginary avatar of yourself in some sort of fictional/dream world.
By imagining yourself into fiction, you can imagine what feelings you would have. In this way, you can receive the feelings that that imaginary you would have, provided you're sufficiently immersed. This is the love of semi-ironic waifuism.
Much more simply, though, waifus are just characters that are someone's favorite in terms of how cute or attractive that person finds them.