Complex sentence: This was because Sunstreak's heat generating powers would cause severe harm to anyone she came in close contact with but Schaub's powers meant he was completely unaffected by heat and therefore an intimate relationship was possible.
Split into simpler sentences: This was because Sunstreak's heat generating powers would cause severe harm to anyone she came in contact with. Schaub, however, was completely unaffected by heat and therefore an intimate relationship was possible.