Jairus
Author of FFVII: Lifestream & FFVII: Reflections
Aerith's death motivates Cloud to action more then anything else regardless of your choices and his attraction to Tifa, his need to impress her is what motivated his true self to join SOLDIER, hide his identity when he returned to his hometown and pretend to be SOLDIER when he reunites with Tifa in Midgar. Your dialogue options can give the girls the cold shoulder yes, but you really do not have the ability to create a version of the story where his feelings towards Tifa and Aerith are portrayed as purely platonic in the original game and I'd be very, very, very surprised if they go that route in the remake.
This does not mean he can't feel anything for anyone else, no. I just don't think Jessie will be a third option, as in mutually exclusive to pursueing Aerith and Tifa romantically.
Except that in Part 1, neither Aerith nor Tifa can get that far with him, and Aerith's death won't happen for at least another game, perhaps two, and the revelations about Cloud and Tifa in the lifestream may be farther away even than that. When I say third option, I was referring to Part 1 only and in terms of that game only, since that's the only game Jessie will be in. Including her as a possible third choice in the affection mechanic for Part 1 only doesn't have to be done in an overt way but, as I've already said, the scenes and events relating to it can be done in a more indirect fashion like Aerith and Tifa's arcs in the OG, where what we see is left to player interpretation and choice and nothing is ever really overtly confirmed. Being a third option doesn't have to be a joke like it was with Yuffie, is all I'm saying, nor does it have to harm the larger story, especially if it's optional as any path in the affection mechanic would be.