This is the way I see it.
"Sexual harassment" is defined not by actions, but by context.
Needless to say, what is appropriate behavior at home with your significant other is not necessarily appropriate at work - but what I mean by context is more inclusive.
Let's say you're at work, and you're hitting it off really well with one of your co-workers. One day after work, you both end up at a bar for a celebration of some kind, maybe a co-workers birthday, or a Christmas party or whatever. You spend the evening talking and flirting - she laughs heartily at your jokes and touches your hand. You guys stay till the bar closes, and when you guys are standing outside waiting for an uber, you lean in for a kiss.
Now, I'm going to re-work that hypothetical.
Let's say you're at work, and you've got a huge crush on one of your co-workers. Every time you see that person in the coffee room, you try to stroke up a conversation, but it never seems to work. Every time, she appears uncomfortable and awkward, and you feel the same way. One day, you hear about an office party after work, and think "there's my chance". You ask the girl if she s going to come - maybe even pressure her to come. When you guys are at the bar, you try to monopolize her time, keep buying her drinks and flirting with her. She laughs at some of your jokes, but it's a hollow laugh, and she keeps looking around, as if she's looking for someone. Finally, she says she has to go home. You offer to leave with her - and while you're both waiting for an uber, you lean over and stick your tongue down her throat.
Explicitly, both of the those narratives are the same. The same primary physical events occurred.
One is appropriate, one is not. I met my girlfriend of 8 years in essentailly that situation.
The difference is in the context - the implicit facts of the situation.
In our culture, it is generally the role of the man to make the first "move". Because of that, it's the responsibility of the man to read the situation correctly - and if you misread it, know how to extract yourself gracefully. With great power comes great responsibility.