As the person in thread above has read more VNs than you less VNs got recommended, there is all of the VNs I really enjoyed that's got heavy focus on romance.
Anything KEY, all of it is good in my opinion, but if you want me to pick 3 than i'd say Little busters, Rewrite and Clannad, if you want me to pick one than I wouldn't have been able to.
Grisaia no Kajitsu has som focus on romance is a really good VN in my opinion.
Symphonic rain, it's a great heavy romance VN, I recommended it in the thread mentioned above and ill do so again, the gameplay is optional so don't let that turn you away.
Katawa Shoujo, it's my favorite VN, probably mostly from nostalgia but that doesn't mean it's not great, it's one of the more popular starter VNs as ive seen and it's heavy romance.
All of these are really good romance VNs that in my opinion is a must read for someone that like romance. Clannad may not be 2007+ new but it's still a good VN and you shouldn't let that alone get in your way, only Grisaia and Katawa Shoujo has H-scenes if that's what you ment with 18+ but still worth to read in my opinion.