I don't think there's any doubt that BM/SM had an unhealthy relationship prior to relocating to Colorado in 2018. But I think there were a couple of differences after arriving in Colorado. First, MM2 was only age 13/14 during her last years in Indiana where she was settled, had her own friends, when her older sister went away to Univ-- and the parents were more likely to shield her of any problems based on her age.
Second, I think that by the 2018 date that SM sent the infamous "Howdy Stranger" message to JL, SM was truly detached from BM, and the gap only widened from that date until her death. IMO, from the date the family arrived in Colorado, both SM and her parent's relationship appeared different to MM1-- to the point where according to SM, she verbalized how she just wanted her "old family" back.
Relative to SM being different (compared to BM), she was becoming seriously ill, and somewhere in between she'd become distracted (with JL) and no longer trying to please BM, MM1's beloved hero. We also know that BM wasted no time in burdening MM1 with his childish, sadness. JMO
I agree and below commentary may give insight, too...
Suzanne's sister was interviewed last year and commented on how she saw the Morphew's relationship.
A few takeaways:
BM and SM were the hometown golden couple
Families excited about their marriage
Suzanne's family so appreciative for the care Barry gave her during first bout of cancer
BM had a good relationship with Suzanne's father, mother and stepfather
GM treated BM as well as his own sons
BM and SM first home was a cute little rental I believe, then they built the custom home in Indiana which Suzanne loved
Many good memories made in their large Indiana home.
Examples given of BM being a doting father.
Suzanne's beloved stepfather died then her mother died
SM took her mother's death hard
SM mother and stepfather a positive influence and stabilizing factor in Barry and Suzanne's life
The Morphew marriage may have felt the loss of their presence
Morphews had a lot materially which may have brought stress to marriage
Barry dominant/Suzanne reserved
Few years before move to Colorado marriage began to deteriorate
Decision to move from Indiana to Colorado at the time they did seemed sudden
Suzanne seemed pleased about the house and picked-out furnishings
Suzanne's sense of self was relative to a role... daughter, wife, mother, sister, friend
She was becoming independent and gaining a sense of self
Suzanne sent the list of grievances May 8th
Saturday afternoon May 9th MMB (SM sister) had an internal sense that something bad had happened to Suzanne