While most continuities that include gendered Transformers only mildly hint at romantic relationships, the Beast Wars/Machines franchise
(and G1 cartoon by extension),
includes a very definitive romantic relationship between Silverbolt and Blackarachnia.
At first, the emotional attachment is one-sided, with Silverbolt professing his love for Blackarachnia, but over time, the relationship is solidified, and they both profess their love for each other.
While no sexual reproduction topics are ever touched, there are scenes in the show where they kissed.
Specific to G1, the cartoon heavily implies that there is a romantic relationship between Orion Pax/Optimus Prime and Ariel/Elita One.
Looking at crossing species...
In The Girl Who Loved Powerglide, Powerglide appears to form a romantic attachment with Astoria.
In Seachange, Seaspray falls in love with the humanoid Alana.