It simply means.."If you love me..." (사랑한다면):)
sarang : 사랑
han da: 한다
myun : 면
"~면" can be translated as "if" or "when" according to contexts.:)
As for "do you love me?", it can be "나(를) 사랑해?" or just "사랑해?" with a question mark.
(Al’afw!)
For your additional question,
1) Subjects or Objects are often left out only if they are quite evident in sentences,but
if you insist..I can say "(당신이 나를) 사랑한다면"
the subject : 당신+이 - you
the object : 나+를- me
In terms of grammar, we put markers right after subjects or objects like "가/이","를/을".
2) "좋아한다면" can be "if you like me" so Yes, you're right.:)
3) "if you go.." can be "gan da myun":)
as in "gan da myun", the subject "당신이" or "네가" omitted.:)