1st BIB
Agreed, there are some wild theories floating around and some that absolutely seem unrealistic. But given that OP's version isn't realistic unless you wish to twist your brain into hocus pocus mode, it is pretty reasonable that the imagination would run wild with this one. Something happened that night that led to up to the events that unfolded in the murder of a defenseless woman. At this point, IMO, none of us do nor will we ever know what those events were. Given that assumption, it is reasonable that theories get explored, as ludicrous as they may seem.
Bottom line though - a young woman is dead after been shot in a horrific fashion behind a closed door. She knew the truth but, so tragically, isn't here to tell the court. I might would believe somehow, someway, OP got up and shot her by accident if he'd give a straight answer instead of the circus we're witnessing currently. He also might have garnered more respect if he were not trying to get away with and relieved of any responsibility for all charges against him.
2nd BIB
1. No evidence of these two being in love at the time of her death. Her message to him 1.5 weeks prior said she was the girl who fell in love with him - past tense. She also wondered if they couldn't give each other what they need. Given that RS seemed like the kind of woman who mostly spread lovey dovey written messages, that one long diatribe to OP about his behavior (and her being scared of him at times) cannot simply be shrugged off as normal relationship interaction. She made a point in that, a valid one and one that I think was an omen to the morning she died.
2. OP said originally that they were deeply in love but when breaking down on the stand, he said words to the effect of "someone I cared for" - another inconsistency. Nothing points to them being deeply in love or her being loved.
3. No plans to spend VD together. No gift for RS. I find it implausible that while being deeply in love, either of these facts would be present, especially for a couple in their 20s.
But these are just my thoughts...