Hi,i will give this a quick shot.From looking at this i see pluto is heavily aspected with a lot of conjunctions here.Pluto can lead to the " fasination" as you have described.It makes one intense and very passionate towards the individual!.It is conjuncting both venus and sun ,which makes this a very significant relationhsip for you.It also squares the moon in this composite as well,which could mean your emotions here are very intense,and and perhaps u feel this realtionship "changes" you in some way.
Also pluto rules over the 8th house as welll,just giving it way more scorponic influence!!!This feels "fated " to you perhaps,where it may feel like this is your everything!
This realtionhsip is also significant being as there is a 7th house stellium there as well which is libras natural house.In the 7th makes it especially important to want to relate to another person which cement all that deep,intense,sometimes dark pluto stuff.
Im still a student so i hope this helped some!!